A modern aquarium hobbyist is usually interested in all facets of aquatic life. The problem regularly encountered by the owners of small and medium size tanks of 20 gallons or less is that water conditions therein are extremely unstable. Slight overfeeding, filter clogging or even statistical fluctuation in the pH and red ox potential ruin whatever delicate equilibrium there may be in the tank. Obviously, the immobile invertebrates such as corals are the most vulnerable species to any adverse local changes in the environment since they are incapable of adjusting their position. Conventional gravity trickle down columns where water is pumped from the bottom layers and is allowed to seep down through a stack of filters have proved to be inefficient as purifying and aerating systems unless the column is so high that it becomes cumbersome in a medium size aquarium. Another drawback of these devices is that they have no provisions for an intensive removal of dissolved noxious gases that are the products of a fish metabolism. Besides, in all conventional aquarium maintenance systems the filtering media are constantly immersed in water which facilitates the accumulation and growth of algae even at a high flow rate of water in the tank and through the filter. This clogging is yet another major intrinsic problem of gravitational filters along with a relatively slow gas transfer through a small gas-liquid interface. These difficulties are compounded by the additional fact that in order to preserve his or her delicate species, the hobbyist has to consider the position of the filter in the tank or the vibrations caused by a necessarily powerful pump.